The paper reports computational and experimental investigations carried out to control of laminar flow separation in LP turbine cascade blades at low Reynolds numbers. T106 LP turbine blade profile with a chord of 60 mm and blade spacing of 48 mm was used. The blade Zweifel loading factor was 1. 03. Passive separation control device of Gurney flaps (GFs) of different shapes and sizes were used. Computations were carried out in Ansys-CFX. A two-equation eddy-viscosity turbulence model, shear stress transport (SST) was considered for all the computations along with gamma-theta (transition model. Computations were carried out for five different Reynolds numbers. Lift coefficient, total pressure loss coefficient, overall integrated loss coefficient and ratio of lift coefficient to overall integrated loss coefficient were used as a measure of aerodynamic performance for the cascade. From the computations, Flat and Quarter Round GFs of heights of 1. 33% of chord were identified as the best configurations. Experiments in a seven bladed cascade were carried out for these configurations along with the basic configuration without GF at five Reynolds numbers. Experimental results agreed well with the computational results for these three cases at the five Reynolds numbers.

The study of intelligent design methods is becoming a hot topic for the design of turbine cascades. This paper proposes a data-based policy model to achieve intelligent design. To gain a high-quality policy model, empirical equations and "space extending + elitism" are adopted to dynamically optimize database. This guarantees the quality of the model. Compared to traditional optimization design approaches, the proposed method relies on less human experience to design a turbine cascade. Ten different turbine cascades are used to verify this method. Results show that, aerodynamic performance of the cascades redesigned is either the same as or better than that of the traditional cascades. The computing time is reduced by more than one order of magnitude compared to a "CFD + optimization algorithm" or "surrogate model + optimization algorithm" method. With the advantages in computing time and intelligence, the proposed novel method shows the possibility of replacing traditional design methods.

In the course of expansion in turbines steam nucleates to become a two phase mixture, the liquid consisting of a very large number of extremely small droplets carried by the vapor. Formation and subsequent behavior of the liquid lowers the performance of turbine wet stages. The calculations were carried out assuming that the flow is two dimensional, compressible, turbulent and viscous. A classical homogenous nucleation model applied for the mass transfer in the transonic conditions. The aim of the present study is investigation of outlet pressure effect on second phase generation in a steam turbine. The maximum and minimum of droplet numbers have been achieved and nucleation zone has been specified in blade passage. Pressure profiles around the blades are compared with the experimental data and good agreement is observed. Results show that the most condensation is on the suction surface of blade and it grows by decreasing the downstream pressure.

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Secondary air bled from the compressor which bypasses the combustion chamber is used to seal the turbine components from incoming hot gas. Interaction of this secondary air or purge flow with the mainstream can alter the flow characteristics of turbine blade passage. An in depth analysis of secondary loss generation by purge flow in the presence of upstream disturbances has huge relevance. The objective of present study is to understand the aerodynamic and thermal effects caused by the purge coolant flow in the presence of an upstream wake. A linear turbine cascade is selected for the computational study and a stationary cylindrical rod which resembles the trailing edge of nozzle guide vane is kept 20 mm before the leading edge to generate the upstream wake (or disturbance). Purge flow disturbances includes strong formation of Kelvin-Helmholtz vortices at trailing edge and additional roll-up vortices at leading edge. Detailed analysis is carried out by varying the velocity ratios as well as the ejection flow angle. Higher velocity ratio and perpendicular coolant ejection reduces the mainstream axial momentum which enhances the passage cross flow. Even though the mass averaged total pressure loss is linearly dependent on the velocity ratio, a reduction in the ejection angle brings down the loss coefficient at the blade exit. A lower ejection angle will improve the film cooling effectiveness also. The presence of purge flow causes an increase in the overturning and underturning.